Patent specification U.S. Pat. No. 6,781,524 discloses a position detection system for vehicles which move along a travel path. The known system comprises a magnetic element which is respectively arranged at the vehicles. Sensor coils are arranged on the travel path. If a vehicle crosses such a sensor coil with its magnetic element, a magnetic flux is generated in the sensor coil by means of the magnetic element. The magnetic flux may then be determined by measuring a sensor coil voltage so that a presence of the vehicle above the sensor coil may be detected.
A disadvantage involved herein is e.g. that considerable time passes before the vehicle position may be determined on the basis of the measured sensor coil voltage. The reason for this is particularly that a continuous periodic voltage signal is applied to the sensor coil so that for the purpose of position detection only a continuous measuring signal is provided, wherein in this context the envelope of the measuring signal is determined over the course of several periods, which takes up a considerable amount of time.
The publication US 2002/0049553 A1 discloses a linear motor comprising a stator and an armature. The armature comprises several permanent magnets. The stator comprises two Hall sensors which are arranged at a distance from each other and which serve to detect the position of the armature and to determine a position error of the armature. The disadvantage of this known configuration is particularly that unknown structural distances between sensor elements may not be detected.
The known systems are furthermore disadvantageous insofar as a distance exists between the two sensor coils for structural reasons. The distance is usually unknown or it may change during operation, respectively. For example, a change of temperature may have the effect of a changing distance between two sensor coils or the two Hall sensors. However, a distance which is not exactly known usually results in that a position of the vehicle or of the armature may not be precisely determined. This may furthermore result in the movement of the vehicle or of the armature exhibiting irregularities, e.g. jerky movements of the motor vehicles or of the armature. Thus, it is not possible to control a smooth movement of the vehicles or of the armature.